1. Field of the Invention
The present invention relates to a perovskite oxide material, a ferroelectric compound containing the perovskite oxide, a piezoelectric body formed of the perovskite oxide, a piezoelectric device using the piezoelectric body, and a liquid discharge device using the piezoelectric device.
2. Description of the Related Art
Currently, the piezoelectric devices constituted by a piezoelectric body and electrodes are used, for example, as piezoelectric actuators installed in inkjet recording heads. In such piezoelectric devices, the piezoelectric body expands and contracts in response to increase and decrease in the strength of an electric field applied from the electrodes to the piezoelectric body. For example, the perovskite oxides such as PZT (lead titanate zirconate) are known as materials suitable for the piezoelectric body. The piezoelectric materials are ferroelectric materials, which exhibit spontaneous polarization even when no electric field is applied.
Incidentally, in consideration of the environmental load, the lead content of the perovskite oxide is preferably small, and more preferably zero. Therefore, development of new lead-free perovskite oxides exhibiting higher piezoelectric performance is proceeding.
Japanese Unexamined Patent Publication No. 2005-047745 (hereinafter referred to as JP2005-047745) discloses, in its claim 1, a piezoelectric ceramic containing first, second, and third compounds, where the first compound has a rhombohedral perovskite structure, the second compound has a tetragonal perovskite structure and contains barium titanate, and the third compound contains at least one of the bivalent metal elements of Bi, Mg, Fe, Co, Ni, Cu, and Zn, at least one of the tetrad metal elements of Ti, Zr, and Sn, and oxygen. In addition, JP2005-047745 discloses, in its claim 3, bismuth sodium titanate as the first compound.
Japanese Unexamined Patent Publication No. 2002-321975 (hereinafter referred to as JP2002-321975) discloses, in its claim 1, a piezoelectric ceramic containing a compound having a rhombohedral perovskite structure, a compound having a tetragonal perovskite structure, and a compound having a monoclinic perovskite structure. In addition, JP2002-321975 discloses, in its claim 6, a concrete composition of the piezoelectric ceramic containing first, second, and third oxides, where the first oxide contains bismuth sodium titanate, the second oxide contains at least one of bismuth potassium titanate and barium titanate, and the third compound contains silver niobate.
Japanese Unexamined Patent Publication No. 2008-098627 (hereinafter referred to as JP2008-098627) discloses, in its claim 1, a piezoelectric device containing a piezoelectric body formed of a perovskite oxide expressed by a compositional formula, (Bi, Ba) (M, Ti)O3, where M represents one of or a combination of ones of the elements Mn, Cr, Cu, Sc, In, Ga, Yb, Al, Mg, Zn, Co, Zr, Sn, Nb, Ta, and W. In addition, JP2008-098627 discloses, in its claim 5, a piezoelectric device containing a piezoelectric body formed of a perovskite oxide expressed by a compositional formula (Bi, Ba) (M′, M″, Cu)O3, where M′ represents one of the elements Nb, Ta, and W, and M″ represents one of or a combination of ones of the elements Mn, Sc, In, Ga, Yb, Al, Mg, Zn, Zr, Fe, and Sn. Further, JP2008-098627 discloses, in its claims 3 and 7, a crystal structure of the piezoelectric body in which at least two of the tetragonal, rhombohedral, pseudo cubic, orthorhombic, and monoclinic crystal phases are mixed.
Japanese Unexamined Patent Publication No. 2008-263158 (hereinafter referred to as JP2008-263158) discloses, in its claim 1, a piezoelectric device containing a piezoelectric body formed of a ABO3 perovskite oxide composed of Bi as the A-site element and two B-site elements, and at least two of the tetragonal, rhombohedral, pseudo cubic, orthorhombic, and monoclinic crystal phases are mixed in the ABO3 perovskite oxide. In addition, JP2008-263158 discloses, in its claim 2, a composition of the ABO3 perovskite oxide, which contains BiCoO3 as a constituent, and at least one of the elements Sc, Al, Mn, Cr, Cu, Ga, In, Yb, Mg, Zn, Zr, Sn, Ti, Nb, Ta, and W as at least one other B-site element. Further, JP2008-263158 discloses, in its claim 3, a composition of the ABO3 perovskite oxide, which contains BiInO3 as a constituent, and at least one of the elements Sc, Al, Mn, Fe, Cr, Cu, Ga, Yb, Mg, Zn, Zr, Sn, Ti, Nb, Ta, and W as at least one other B-site element.
The conventional piezoelectric devices commonly use the field-induced strain (i.e., the piezoelectric strain along the direction of the spontaneous polarization axis) caused by application of an electric field along the direction of the spontaneous polarization axis. (That is, the direction of the applied electric field is identical to the direction of the spontaneous-polarization axis.) However, the magnitude of strain produced by only the conventional field-induced strain is limited, and therefore demands for a greater magnitude of strain have been increasing.
A group including one of the present inventors Yukio Sakashita discloses, in U.S. Patent Application Publication Nos. 20090267998 and 20080265718 (which are hereinafter respectively referred to as US20090267998 and US20080265718) and other documents, piezoelectric devices each constituted by a piezoelectric body having domains the phases of which can transition to different phases when an electric field is applied to the piezoelectric body in a direction different from the direction of the spontaneous-polarization axis. Further, the present inventors disclose, in U.S. Patent Application Publication No. 20080074471 (hereinafter referred to as US20080074471) and other documents, a piezoelectric device constituted by a piezoelectric body having domains the polarization axes of which can be reversibly rotated by a non-180-degree angle by increasing or decreasing the electric field applied to the piezoelectric body in the direction different from the direction of the spontaneous-polarization axis.
In the systems in which the field-induced strain and/or the reversible non-180-degree domain rotation can occur, a piezoelectric strain greater than the conventional field-induced strain can be achieved in the direction of the spontaneous-polarization axis when an electric field is applied along the direction of the spontaneous-polarization axis. In such systems, a great magnitude of strain can be achieved even at a relatively low strength of the electric field.
Further, JP2008-263158 states in its paragraph 0041: “It is preferable that the tetragonal crystal and at least one of the rhombohedral, pseudo cubic, orthorhombic, and monoclinic crystals are mixed in the piezoelectric body. In the case where a piezoelectric body having the above crystal configuration contains (100)-oriented domains, the (100) orientation can be changed to the (001) or (010) orientation by applying an electric field to the piezoelectric body, so that high piezoelectric performance can be achieved.”